As patients live longer and are diagnosed with chronic and often debilitating ailments, the result will be an increase in the need to place protein therapeutics, small-molecule drugs and other medications into targeted areas throughout the body that are currently inaccessible or inconvenient as sites of administration. For example, many vision-threatening diseases, including retinitis pigmentosa, age-related macular degeneration (AMD), diabetic retinopathy, and glaucoma, are incurable and yet difficult to treat with currently available therapies: oral medications have systemic side effects; topical applications may sting and engender poor compliance; injections require a medical visit, can be painful and risk infection; and sustained-release implants must typically be removed after their supply is exhausted (and offer limited ability to change the dose in response to the clinical picture). Another example is cancer, such as breast cancer or meningiomas, where large doses of highly toxic chemotherapies such as rapamycin or irinotecan (CPT-11) are administered to the patient intravenously, resulting in numerous undesired side effects outside the targeted area.
Implantable drug delivery systems, which may have a refillable drug reservoir, cannula and check valve, etc., allow for controlled delivery of pharmaceutical solutions to a specified target. This approach can minimize the surgical incision needed for implantation and avoids future or repeated invasive surgery or procedures. Refillable ocular drug pumps, for example, usually hold less than 100 μL, are much smaller and more difficult to access post-implantation than other implantable pumps, such as those used for intrathecal injections or insulin therapy.
An implantable drug-delivery pump may incorporate telemetry to facilitate communication with an external monitoring device and wireless charging of the battery powering the implanted device via inductive coupling. In particular, the operating parameters of the implantable pump may be non-invasively adjusted and diagnostic data may be read out from the implantable pump to the external monitoring device through signals transmitted by and received from the telemetry device. During a scheduled visit, a physician may place the monitoring device near the implantable pump and send signals thereto. The implant, in turn, adjusts pump parameters and transmits responses to the monitoring device. By incorporating wireless charging technology, electronic medical implants benefit from a smaller total footprint by reducing the battery size.
Typically, the telemetry circuitry comprises a coil antenna that transmits and receives signals via inductive coupling. A number of parameters characterizing the efficiency of the coil antenna, e.g., the resonant frequency, gain, quality (Q) factor, and thermal effects (i.e., the Joule effect or heat) are considered when selecting or designing the coil antenna. However, the challenges of designing an antenna small enough to fit within an implant while exhibiting adequate performance characteristics, notwithstanding tissue attenuation that weakens the inductive link, are considerable.